Solid phase extraction is a powerful technology for purifying and concentrating analytes, including biomolecules. For example, it is one of the primary tools used for preparing protein samples prior to analysis by any of a variety of analytical techniques, including mass spectrometry, cryo-EM, nuclear magnetic resonance, x-ray crystallography, cell based assays, and the like. With these techniques, typically only a small volume of highly-concentrated sample is required, however, it is often critical that interfering contaminants be removed from the sample. Thus, sample preparation methods are needed that permit the purification and concentration of samples. Both of these parameters are particularly important for determining structure and function of the biological material such as proteins, polypeptides, and other materials.
Traditionally, high concentrations of a desired analyte are obtained from chromatography columns using the heart-cut method. This involves collecting fractions and determining analyte concentration within each fraction. For a protein analyte, concentration determination can require a spectrophotometer. After the concentration of each fraction is determined, those fractions that contain the highest concentration of analyte are retained. This process is time-consuming, labor-intensive and equipment-intensive and cannot be automated. Therefore, better methods are needed to obtain highly concentrated, pure material for a variety of analytical processes.